Synthesis of cyclopropane



1,22-trichloropropane in any desired manner.

` Also, we may obtain a mixture of 1,3-dichloropropane and 1,2,2-trichloropropane in any desired manner. ,Desirably We obtain this mixture by chlorinating propane, as for example in the processes set forth in the Hass 1r McBee patents Nos. 2,004,072 and 2,004,073 already-referred to, and separating such mixture from the lower and the higher boiling chlorides that are simultaneously produced, by making a iirst cut between e and I' in the table given above and a second cut between y and h in such table.

Having obtained the selected starting material, Whether it 'is i,2,2trichloropropane alone or a mixture of l-dichloropropane and l,?.,2trichlo ropropane, We then treat lt in the general manner set forth in our aforesaid iso-pending applicaties Serial llo. H1429.

This is done by causing the 1,2,2-trlchloropropane, or the mixture of it with l-dichloropropane, to react-With Zine or magnesium or sodium. The following seminar-lying equations show the L3 deld'oropropsne cyclopropene The summarizing equations with magnesium or sodium, or other usable metals, are in general similar.

ln order to obtain simultaneously the reactions indicated in equations l and 2, whatever the metal used, certain conditions oi the reaction should loe maintained. These 'conditions are in 'general those which are necessary for preparing normal alkyl magnesium chlorides from normal alkyl chlorides and magnesium; in that there must be present substantially no compound containing hydrogen displaceable by the metal used under the conditions employed in the reaction, and that temperatiue must be sutticiently high to initiate the reaction. The temperature necessary depends on the metal used, and is highest for eine and lowest for magnesium for a given reaction rate.

also in obtaining those tivo reactions simultaneously, We usually prefer either to use a catalvst to start the reaction or to raise the temperature above the normal boiling point of the 1,3- dichloropropane, or both. li no solvent is used, however, such raising o' 'the temperature involves high-pressure operation and apparatus, which is usually not desired; and therefore We prefer to use a boiling-point-raising solvent which has a boiling point above that oi 1,3-dichloropropane. Any such solvent which'dissolves trimethylene chloride and i,2,2-tridoloropropane may be used which is suitable for use in preparing the Grignard reagent and which is substantially unattacked by the reagents and/or reaction products under the conditions employed. The most erfective groups of solvents are the higher-boiling others, such as diphenyl ether and dibutyl ether, and the higher-boiling hydrocarbons, such as biphenyl. We prefer to use no catalyst with either zinc or sodium; but in using magnesium We may use a catalyst instead of or in addition to heat to initiate the reaction, and in that case we may use a preformed Grignard reagent or any catalyst which is used in preparing the Grlgnard reagent.

Not all of the above conditions need be maintained, however, if it is desired merely to produce 2chloropropene from 1,2,2-trichloropropane, as this latter reaction appears to take place with greater facility than the reaction for the preparation of cyclopropane from 1,3-dchloropropane.

The following are examples of our process:

Example Z: Diphenyl ether, the boiling point of which is 259 C., has a` maximum quantity of zinc dust added to it so that the mixture still stirs fairly easily, and a suicient quantity of either l,2,2trichloropropane or a mixture of 1,2,2- trichl-oropropane and 1,3-dichloropropane to lower the boiling point to the neighborhood of 180 to 210 C. The Whole is heated 'to-that boiling point, with stirring, and a gas is evolved which is almost Wholly the desired 2-chloropropene if the chloride added was 1,2,2-trichloropropane, and is almost Wholly a mixture oi 2-Chloropropene and oyclopropane the mixed chlorides (1,2,2-triohlor0propane and 1,3-dichloropropane) were the added chlorides. As the gas is evolved, additional 1,2,2-trichioropropane or mixture of 1,2,2-trichloropropane and 1,3-dichlorop'ropane is desirahly added, and the boiling point is thus maintained Within the range given. The gas evolved is collected. li the added chloride was 1,2,2-trichloropropane alone, this gas is mainly -chloropropene. But i' the added chlorides were mixed 1,2,Z-trichlor-opropane and l,3dichloro propane, such .gas is mainly mixed Z-ohloropropene and eyclopropane; and in that case the two components oi. the mixture are. separated by rectiiication, as is readily7 possible because of the Wide diderence between their boiling points, to obtain separately both cyclopropane and 2- chloropropene.

The process or' removing the tivo chlorine atoms by the zinc is continued as long as the reaction proceeds actively; out in time the zinc particles become coated with the zinc chloride which is formed as a Toy-product, and the reaction gradually slows down. lihen this occurs, the zinc mass is separated from the solvent, as by decantlng or lterlng, and washed with any solvent, such as ethyl ether, which dissolves the zinc chloride `from the zine particles; whereupon the clemed zinc dust may be used again. The zine chloride, separated as such by evaporation oi the ethyl ether, is a valuable oy-product.

Example 2: Biphenyl, which boils at 250 C., has from 57% to 10% oy Weight of metallic sodium added to it, and then enough 1,2,2-trichloropropane, or mixture of 1,2,2-trichloropropane and LB-dichloropropane, to reduce .the boiling point to the neighborhood of to 200 C. Some reaction occurs at room temperature, although a very slow one; but the reaction may be accelerated loy heating, desirably to the boiling point without danger that it will become too violent. In either instance, slowly in the cold and more rapidly on heating, a gas is evolved which is rich in 2-chloropropene or in mixed 2-chlorovpropone and oyclopropane according to the start- C., has magnesium turnings or powder added to it, in any desired amount, so long as the amount of solid material either originally present -or produced in the reaction is kept lsuiiicieutly small toavoid interference with stirring. Then a small amount of 1,2,2-trichloropropane, or of mixed l,2,2,`trichloropropane and 1,3-dichloropropane, is added, usually not to exceed 5%, and the mass heated until boiling occurs. A gas is evolved, which is rich inl Z-chloropropene or in mixed 2- chloropropene and cyclopropane, according to the starting chloride or chlorides-used. As the reaction proceeds, more of the starting chloride or chlorides may be added, either slowly and continuously or in small increments. After the reaction is going well, the heating may be discontinued, :lor the reaction is exothermic. 1i.' desired, a small amount of a catalyst may be added initially to start the reaction. Suitable catalysts are ethyl iodide or tree iodine, or preferably a preformed Grignard reagent.

ln all these examples, and especially in examples 2 and 3 where sodium and magnesium are used, it is desirable to maintain rather rigorously anhydrous conditions. This is also desirable when zinc is used, although not so essential; but in any case there should be substantial freedom from water or other substance which contains hl drogen displaceable by the nictal used under the conditions employed in the reaction.

A feature oi distinction of the process of the present invention to which it is desired to direct attention, is that, somewhat surprisingly, twov en trely dissimilar' dechlorination reactions take place simultaneously under inherently identical conditions, one involving a ring closure (to form cyclopropane, and thus changing a paramnie hyn drocarbon skeleton to a naphthenic one), and the other involving a direct unsaturation {to iorm d-chloropropene, and `thus changing a paramnic hydrocarbon skeleton to an olenic one). r-

, dinarily it would be inferred that two such disunder the conditions employed in the reaction,

Ysible to obtain a number of advantages.

and can he made to give fairly good yields. Yet the reaction is somewhat slow, and that slowness has some disadvantages in commercial operations. i

We have also found that by varying the procedure somewhat, as will now appear, it is pos Among such advantages are an increased speed of reaction, an increased yield of Z-chloropropene or o mixed cyclopropane and Z-chloropropene, a lower temperature of reaction, and the elimination oi the necessity oi avoiding components containing hydrogen replaceable by zinc.

In the co-pending application led by us and Earl W. Gluesenkamp, Serial No. 85,048, ied June 13, 1936, it is shown that cyclopropane may be produced by the simple' reaction of zinc with either l-chloro-S-lodopropane or 1,3-di-iodopropane, by the following reactions:

on, (3) cH,C1oHf-cn,1-1zn n,C-cu,+zncu /cm (4) CHg-'GHz-*CHzI-lzll H3C \CHI+ZBI3 In that Hass, Hinds Giuesenkamp applicau tion Serial No. 85,048 it was also shown that one or both of the chlorine atoms of l-dichloro propane (trimethylene chloride) may be replaced by iodine by a metathetical reaction with sodium iodide, to yield l4chloro-3-iodopropane and i,3 di-iodopropane respectively. as shown by the iollowing reactions:

(e) euromunt-Lentement@ cnd--onz-cnir-l-anaol it was pointed out in that application that suitable solvents for carrying out this reaction are acetone and ethanol; since sodium iodide is solu ble in those solvents, while sodium chloride is practically insoluble in them .and so when toed is removed from the reaction by precipitation. The reactions shown in equations 5 and d y be merely summer-icing reactions, and we be lieve they are; for we believe that what actually happens is that the sodium iodide ionioes to yield Y:free iodide ions which are present in the sodium solution in alcohol, :and that it is these iodide lons which react with the l-dichloropropane, as shown by the lollowing eduations:

ln that Hass, Hinds tr Gluesenkaimp applica-1 tion Serial No. 85,048 it was also pointed out that it is possible to regenerate sodium iodide, or the iodide ions therefrom, in the reaction, by the use of a much cheaper reagent; so that such sodium iodide takes on the nature of a catalyst rather than a reactant in the total reaction, and only a small quantity of sodium iodide need be used. That regeneration is obtainable by any reagent that is capable of reacting with zinc iodide to yield a more highly ionized iodide; for such a reagent reacts with the zinc chloroiodide or the zinc iodide of equations 3 and 4 to reproduce the iodide ions. Quite a number of reagents will do this, and two simple ones are sodium carbonate and acetaxnide.

As the result of those things, it was pointed out in said Hass, Hinds 8i Gluesenkamp application that not only can cyclopropane be produced by thesimple reaction of zinc with either l-chloro- 3-iodopropane or 1,3-diiodopropane as shown in equations 3and 4, but that in addition it is possible to obtain a rapid production of cyclopropane from 1,3-dichloropropane by first converting the latter into l-chloro--iodopropane and/or 1,3-cliiodopropane by the use of free iodide ions and then reacting the product so obtained with zinc, while at the same time regenerating in the solution the iodide ions to. maintain the reaction rate without requiring sodium iodide `in more than catalytic amounts.

We have now discovered the surprising factV that similarly the production of 2-chloropropene from 1,2,2-trich1oropropane may be made more rapid by the use of free iodide ions, and then rewithout requiring the sodium iodide in more than catalytic amount.

In consequence, since this increase in rapidity occurs both in the production of' cyclopropane from 1,3-dich1oropropane (as set forth in the aforesaid Hass, Hinds 85 Gluesenkamp applical@ tion) and in the production of 2-chloropropene from 1,2,2-trichloropropane, a corresponding rapidity of reaction is obtainable in convertinga mixture of LS-dichloropropane and LZ2-trichloropropane into a mixture of cyclopropane 5 and 2-chloropropene.

-An example will show the general technique: 360 gm. of acetamide, @.02 mole of sodium iodide, 0.377 mole of sodium carbonate, and 1.1 moles of zinc dust are placed in a -liter three-neck round-bottom flask fitted with a mercury-seal stirrer, a dropping funnel, and a redux condenser in the respective necks. The reflux condenser is connected at the top to an outlet tube leading to the apparatus for collecting the gas. .any suitable means may be used to remove any ammonia which results from the reaction of traces of moisture with the acetamide. i charge of 0.832 mole of ,2,2-trichloropropane, or of a mixture of ,3-dichloropropane and LZ2-trichloropropane, is placed in the dropping funnel, and admitted to the body of the flask drop by drop over a period of about five hours while the temperature of the flash is maintained at about "125 C desirably Within 5 of that temperature.

The gaseous product which passes from the top of that reflux condenser and is collected in the collecting apparatus is Z-chloropropene if only 1,2,2-trichloropropane was dropped in through the dropping funnel, and is a mixture of cyclo- 4@ propane and Z-chloropropene if it was a mixture of i-dichloropropane and i,2,2-trichloropropane which was dropped in through the dropping funnel; in which latter case the two components of the resultant mixture may be separated by 45, rectication as has already been described.

Another example of our invention is as follows:

An apparatus is used consisting of a 500 ml.

round-bottom three-neck iask, a condenser, and

a motor-driven mechanical stirrer. By means of no glass tubing, gases are conducted from the top of the condenser into a straight-tube condenser kept in a bath at about 79 C.

`This ask is charged with 1,20 ml. oi' 75% aqueous ethanol, 6.1 mole of 1,2,2-trichloropromi pane or of a mixture of 1,3-dichloropropane and 1,2,2-trichloropropane, 0.1 mole of anhydrous sodium carbonate, 0.2 mole of zinc dust, and i/Gll mole of sodium iodide. The flask containing this charge is heated on a steam bath for twelve a@ hours, and crude 2-chloropropene (if only 1,2,2-

trichloropropane was used) or a mixture of crude cyclopropane and 2-chloropropene (if a mixture of 1,3-dichloropropane and 1,2,2-trichloropropane was used) is evolved and collected. The gas so 55 obtained is puried in well-known ways; and if it is a mixture of cyclopropane and Z-chloropropene the components of that mixture are separated by rectification.

. We claim as ourl invention:

70 1. The process of producing cyclopropane,

which comprises causing a mixture of 1,3-dichloropropane and 1,2,2-trich1oropropane to react with a metal exhibiting an aiinity for chlorine, toyield a chloride of the metal and a 75 mixture ofcyclopropane and 2-chloropropene,

and fractionating to separate cyclopropane from the mixture so obtained.

2. The process of producing cyclopropane and 2-chloropropene, which comprises causing a mixture of LS-dichloropropane and 1,2,2-tri- 5 chloropropane to react with a meta-l exhibiting an affinity for chlorine, to yield a chloride of the metal and a mixture of cyclopropane and 2- chloropropene, and fractionating the mixture of cyclopropane and Z-chloropropene into its com- 10 ponents.

3. The process of producing cyclopropane, which consists in causing a mixtureoi 'n3-dichloropropane and 1,2,2-trich1oropropane to react with a metal emibiting an amnity for chlo- 15 rine, to yield a chloride of the meta-i .and a mixture of cyclopropane and Z-chloropropene, and subjecting said last-named mixture to rectification to obtain the desired cyclopropane.

rShe process or" preparing cycopropane, 2@ which consists in chlorinating props a mixture of chlorides o propane, e said mixture of chlorides oi propane to rectification to separate from lower-boiling racticns and from higher-boiling fractions a riddle fraction 25 consisting mainly oi LS-dichioroprop-ane and ,2,2trichloropropane, causing at middle iraction to react With a metal exilA Eng an ainity for chlorine to yield a chloride of that metal and a mixture of cyclopropane and 2--cidcpropene, and iractionating to separate crclopropaneirom that last-named mixture of cycloprcpane and 2- chloropropene.

5. The process of producing substar cyclopropane from impure 2,3-dichlor that is contaminated n with la-triedpane, which consists in causing said contaminated i,3-dichloropropane to react voith a metal exhibiting an affinity .Tor chlorine to yield a chloride or" that metal and a cyclopropane which 4@ is contaminated `with Z-chloropropene, and subjecting that contaminated cyclcpropane to rectication to separate substantially pure cyclopropane therefrom.

6. The process of producing cyclopropane, which comprises causing a mixture of LS-dichloropropane and ,2,2trichloropropane to react with Zinc, to yield zinc chloride and a mixture of cyclopropane and 2-chloropropene, and fractionating to separate cyclopropane from the mixture so obtained. Y

T. The process of producing cyclopropane and 2-chlo`ropropene, which comprises causing a mixture of LS-dichloropropane and 1,2,2-trichloropropane to react with zinc, to yield zinc chloride and a mixture of cyclopropane and 2-chloropropene, and fractionating the mixture of cyclopropane and 2-chloropropene into its components.

8. The process of producing cyclopropane, which consists in causing a mixture of 1,3-dichloropropane and 1.2,2-trichloropropane to react With zinc, to yield zinc chloride and a mixture of cyclopropane and 2-chloropropene. and subjecting said last-named mixture to rectication to obtain the desired cyclopropane.

9. The process of preparing cyclopropanc, which consists in chlorinating propane to get a mixture of chlorides of propane, subjecting said mixture of chlorides of propane to rectiiication to separate from lower-boiling fractions and from higher-boiling fractions a middle fraction consisting mainly of 1,3-dichloropropane and 1,2,2-trichloropropane, causing that middle fraction t0 react with zinc to yield Zinc chloride u `and a mixture of cyclopropae and 2ch1oro propene, and fractionating to separate cyclopropane from that last-named mixture of cyclopropane and 2-ch1oropropene.

10. The process of producing substantially pure cyclopropane from impure 1,3-dich1oropropane that is contaminated with 1,2,2-'trich1oropropane, which consists in causing said contaminated 1,3-dich1oropropane to react with zinc to yield zinc chloride and a cyclopropane which is contaminated with 2-ch1oropropene, and subjecting that contaminated cyciopronane to rectication to separate substantially pure g54 cyclopropane therefrom.

HENRY B. HASS. GEORGE E. HINDS. 

